test(tests/lean/extra): more tests for equation elaborator
feat(library/algebra/ordered_ring): start on ordered_ring, and minor changes elsewhere
refactor(library/algebra/ordered_ring): add workarounds to improve performance
fix(frontends/lean/structure_cmd): simplify structure names
fix(library/init/logic): expose inhabited basic instances
fix(library/aliases): aliases in sections and contexts
feat(library/data/nat): add "bounded" quantifiers

Later, we will add support for arbitrary well-founded relations
feat(library/logic/quantifiers): add decidable_forall_eq and decidable_exists_eq theorems
fix(bin/ltags): open .ilean files with UTF-8 encoding

fix #376
refactor(library/logic/connectives): rename theorems
refactor(library/logic): rename theorems
feat(library/init): create markdown directory file